A1 -> B1 -> B2 (the menu points back to A1)

Time            | T1       | T2       | T3
----------------+----------+----------+-------------
Tab 1:          | A1 -> B1 |          | [refresh B1]
Tab 2:          |          | A2 -> B3 |
----------------+----------+----------+-------------
Menu points to: | A1    A1 | A2    A2 | A2

// This is executed right before leaving the page
window.onunload = function() {
    if( '{{ A }}' != null )
        var prev_A = '{{ A }}';
    else if (typeof previous_A != 'undefined') {
        var prev_A = previous_A;
    else
        var prev_A = '';
    localStorage.setItem('a', prev_A);
};
// Remove the local storage as soon as you get to this page
localStorage.removeItem('a');

var previous_A = localStorage.getItem('a');